The organisation revealed the “vast majority” of the 43,000 people affected were those who had registered with email addresses and encrypted passwords or had filled in an online form with basic contact details.

It said there was “a very low exposure risk to identity theft or online fraud” with this kind of data.

It advised customers and ABTA members registered on the site to change their passwords as a precautionary measure.

ABTA has also offered people who may be affected a free-of-charge identity theft protection service.